In many medical procedures, various physiological conditions present within a body cavity need to be monitored. These physiological conditions are typically physical in nature—such as pressure, temperature, rate-of-fluid flow, and provide the physician or medical technician with critical information as to the status of a patient's condition.
One device that is widely used to monitor conditions is the blood pressure transducer. A blood pressure transducer senses the magnitude of a patient's blood pressure, and converts it into a representative electrical signal that is transmitted to the exterior of the patient. For most applications it is also required that the sensor is electrically energized.
Some means of signal and energy transmission is thus required, and most commonly extremely thin electrical cables, sometimes called microcables, are provided inside a guide wire, which itself is provided in the form of a tube, which often has an outer diameter in the order of 0.35 mm, and oftentimes is made of steel.
In order to increase the bending strength of the tubular guide wire, a core wire is positioned inside the tube. The core wire also helps to improve “pushability” and “torquability” of the guide wire. The mentioned electrical cables are e.g. positioned in the space between the inner lumen wall and the core wire.
Sensor and guide wire assemblies in which a sensor is mounted at the distal end of a guide wire are known. In U.S. Pat. Re. 35,648, which is assigned to one of the present assignees, an example of such a sensor and guide wire assembly is disclosed, where a sensor and guide wire assembly comprises a sensor element, an electronic unit, a signal transmitting cable connecting the sensor element to the electronic unit, a flexible tube having the cable and the sensor element disposed therein, a solid metal wire, and a coil attached to the distal end of the solid wire. The sensor element comprises a pressure sensitive device, typically a membrane, with piezoresistive elements connected in a Wheatstone bridge-type of arrangement mounted thereon.
As is disclosed in, for example, U.S. Pat. No. 6,167,763, which also is assigned to one of the present assignees, the sensor element can be arranged inside a short tube (usually referred to as a sleeve or jacket), which protects the sensor element and comprises an aperture through which the pressure sensitive device is in contact with the ambient medium. The solid metal wire—which, as also mentioned above, in the art usually is referred to as the core wire—extends through the interior of the jacket and may be provided with an enlarged diameter portion adapted for mounting of the sensor element.
The entire contents of all of the above-described documents are incorporated herein by reference for the methods and devices described therein.
A potential problem with this kind of guide wire mounted sensors is the occurrence of so-called bending artefacts. A bending artefact is a change in the output signal from the sensor that is induced by a bending of the guide wire, rather than being induced by a change in the physical environment surrounding the sensor.
To achieve the desired resistance against bending artefacts, the sensor may be designed and mounted in different ways, the common feature being that it is a cantilevered mounting arrangement that provides the desired resistance against bending artefacts.
The cantilevered mounting of the sensor, however, requires extra machining or wire forming of the core wire at the site where the sensor chip is placed. The careful machining of the core wire into different diameters and different shapes at different portions of the guide wire is a time-consuming process and may be a source of manufacturing mistakes, leading to loss of time and material in the manufacturing process.
In U.S. Pat. No. 6,221,023 is disclosed a sensor mounted on the distal end of an intra-corporal catheter. The sensor includes a chip that is deformable in accordance with pressure applied thereto, strain gauges mounted on the chip, a sensing plate, a projection, a cap and a tube. The projection and the cap transmit pressure applied to the catheter's distal end to the sensing plate and tilt the sensing plate in accordance with the pressure where the strain gauges issue detection signals according to the degree and the direction of the tilting.
The inventors have realized that there is a need for a sensor guide wire wherein the mounting of the sensor does not involve extra machining or wire forming, which thereby is easier and less expensive to manufacture. In addition, a further need is to improve the resistance to bending artefacts, and also to improve the flexibility and bending profile of the distal portion of the sensor guide wire.